I would like to control the PX4 via micropython (ESP32 micro controller) but can just find libraries for python (dronekit-python). MAVlink itself doesn’t seem to be available for micropython, too. So here is my question: Do you think there is any change to shift it over to micropython or must I use a raspberry pi as companion instead?

firmware PX4 works with MavSDK API, while Arducopter is compatible for Dronekit python API.
If you insist to apply PX4, you may turn to MavSDK (python library).
I am working on dronekit-python currently.